This invention relates to the extrusion of products from molten polymers and more particularly, to producing beautifying patterns on the surface of these products.
A variety of products are made from thin polymer material such as polyethylene. For example, small bags are used in the packaging of sandwiches and the like; larger bags are used as shopping bags; and even larger bags are used for containing trash. These bags are typically made from blown polyethylene produced by forcing molten polyethylene through an annular extruding die.
These products frequently show surface texture. It is known that extruding polymers at a critical shear level produces melt fracture. See Trans. Soc. Rheol., 1, 203, J. P. Tordella, (1957); and J. Appl. Polym. Sci., 21, 1177, J. Vlachopulos and T. W. Chan (1977).
My co-workers and I have concluded that melt fracture of linear polyethylene, including linear low density polyethylene (LLDPE), occurs in the die, or as the molten polyethylene emerges from the die.
Polymeric products with uncontrolled random melt fracture texture have poor appearance. However, controlled melt fracture texture can provide a different, pleasing appearance.
It is an object of the present invention to provide extruded products with a decorative melt fracture pattern.
It is another object of the present invention to control the polymer extruding process so that beautifying patterns on the surface of the extruded products are produced.